How long can you have dormant lyme disease for?

Many years: I have had patients who, based on their history, were likely exposed to lyme many years prior to becoming symptomatic, with their symptoms coming on after an injury or other major stress to their system. Once someone seems to have recovered from lyme, symptoms may also recur several years later if they are subjected to great physical or emotional stress, suggesting it was dormant for many years.

Not really "dormant: Dormancy implies "doing nothing"- it doesn't reflect what is actually going on. The term "subclinical" or "undiagnosed" better describes its presence as it does damage to the body, without people realizing its presence in an infected individual.